The present invention relates generally to agricultural implements such as rippers, and more specifically to wheel structure for such implements.
Agricultural implements such as deep tillage rippers often are towed by a large four-wheel drive (4WD) tractor, especially if the implement is a larger unit with nine or more standards. A problem can arise when the operator desires to pull an integral ripper, which is normally mounted on a three point tractor hitch, since many 4WD tractors in the size range necessary are not equipped with such a hitch. It is often desirable to have a means of converting an integral ripper to a pull-type unit. Consequently, a drawn hitch attachment is needed for the larger sized rippers, and compatibility with smaller rippers such as those with five or seven standards is advantageous.
Numerous hitch attachments are available for converting an integral ripper to a pull-type ripper. Such attachments typically include a hitch assembly that pins into the existing lower hitch plates of the ripper. A turnbuckle is placed from the upper link attachment location on the ripper to an upper surface of the hitch to facilitate horizontal adjustment of the machine front-to-rear for compensating for different tractor drawbar heights. Independent wheel packages are generally placed off the front of the ripper, one on each side, with a forward acting wheel arm and dual tandem wheels.
Hitch attachments for conversion from integral to pull-type can produce some very undesirable conditions. A light hitch condition often results from placement of the majority of the implement weight behind the wheels, a condition that produces high vertical hitch loads on the tractor drawbar in the upward direction. The high vertical loads, in turn, produce high axial loads which pass through the turnbuckle. Other negative attributes of the forwardly located wheels include unstable transport conditions and high stresses on certain areas of the implement frame. A further problem with some wheel arrangements is instability or oscillation of the implement while operating in the field as the front of the frame tends to nose downwardly and then rock back upwardly under certain field conditions.
To eliminate some of the problems, placement of the transport wheels near the rear of the machine is helpful. However, numerous obstacles on the rear of the implement frame limit such wheel placement. Placement of the wheels at the rear of the implement creates undesirable moments tending to rotate the front of the frame downwardly. Maintaining proper machine attitude and uniform working depth is a problem.
Using wheels at both the front and the rear of the implement present numerous problems, including the provision of an economically feasible wheel lift and timing system. Hydraulical controls for all the wheels can be expensive and very complex. Manually adjustable gauge wheels often are difficult to fine tune, particularly when the implement is relatively large and heavy. Providing conversion hitch attachments therefore has presented numerous challenges to the implement designer.
A problem with independent wheel modules, regardless of wheel location, is need for structure to keep the wheels timed. A mechanical timing tube is often impractical because of interference with machine components.
It is therefore an object of the present invention to provide an improved attachment structure for conversion of an integral implement to a pull-type implement. It is a further object to provide such a structure which overcomes most or all of the aforementioned problems.
It is another object of the present invention to provide an improved attachment structure for conversion of an integral implement to a pull-type implement which is relatively low in cost and complexity. It is yet another object to provide such a structure having improved stability, better depth control consistency, reduced stress and reduced front to rear instability or oscillation problems compared to at least most previously available structures.
It is a further object of the invention to provide an improved attachment structure for conversion of an integral implement to a pull-type implement having a compact, economical design which facilitates a variety of tool spacings without interference. It is another object to provide such a structure which is compatible with large implements such as rippers with up to nine standards or more as well as with smaller implements such as rippers with five or seven standards.
It is yet another object of the invention to provide an improved attachment structure for conversion of an integral implement to a pull-type implement, the structure having a rearward acting transport wheel and a forward acting gauge wheel. It is a further object to provide such a structure having a simple and inexpensive lift system.
Attachment structure described below for converting an integral implement to a pull-type implement includes wheel modules which can be conveniently mounted at different locations along the implement frame depending on the number and spacing of tools. Each module supports both a forward gauge wheel and a rearward transport wheel. The module includes a lower wheel bucket or channel, in which a rear wheel arm rotates, and an upper mast or tower. The tower captures the base end of a hydraulic cylinder used to raise and lower the rear transport wheels. The tower additionally contains a sliding mechanism for a front gauge wheel yoke. Mounting hardware secures each tower and bucket to the desired location on the front rank tube of the implement.
The transport wheels are located behind the center of gravity of the implement to provide a substantial improvement in stability and reduced frame stress. The placement of the wheels achieves the desired amount of downward force on the tractor drawbar. The forwardly located gauge wheels offset the moment resulting from the ripper standard draft that rotates the front of the implement downwardly to stabilize the machine in working conditions. Normal field working depth is set by lowering the machine into the ground to the desired depth using the hydraulically controlled rear wheels. Cylinder stops are then placed on the depth control cylinders, and the front gauge wheels lowered into contact with the ground. However, because of the weight and size of the implement, fine tuning the gauge wheel position requires considerable force. To economically provide the necessary mechanical advantage, the hitch storage jack is made to double as a gauge wheel adjustment tool. The jack slides onto a post mounted on the upper tower and pushes against a clip mounted on the side of the gauge wheel yoke.
To prevent the transport wheels on the wheel modules from getting out of phase, a hydraulic system includes a parallel circuit with pilot operated check valves on the base or lift end of each cylinder. The check valves lock hydraulic fluid into the base end of each cylinder and prevent uneven loads from changing the relative extension of the cylinders. The pilot is operated off the rod or lower end of each cylinder. Therefore, when the machine is lowered, the check valve opens and allows oil flow out of the base end. An orifice is used to provide the optimum breakoff pressure for the check valve.
The rearward placement of the transport wheels creates very stable transport conditions. The wheel modules can be widely spaced for additional stability. Working depth accuracy and machine stability in the field is greatly improved because of the spacing of the four wheels, and the combination of the front and rear wheel support during tillage operations reduces or eliminates the oscillations of the type wherein the frame noses downwardly and then rocks back upwardly. The rear wheels can be used to set the desired working depth hydraulically. The wheel structure provides excellent support for the frame when the implement includes rear mounted tools such as leveling wheels or rolling basket attachments. By mounting two independent wheels to each wheel module, costs and complexity are minimized. Utilizing the hitch storage jack for gauge wheel adjustment results in a unique, cost-effective and user-friendly drawn hitch attachment. The hydraulic system eliminates need for costly rephasing cylinders and avoids the high reaction forces of a traditional master-slave series circuit. If desired, the hydraulic lock-up valve normally used during storage and machine maintenance can be eliminated because the check valves provide the same function.